feat: bump to NixOS 26.05 (Yarara) — WIP, desktop unverified on hardware

Bumps nixpkgs nixos-25.11 -> nixos-26.05, home-manager release-25.11 ->
release-26.05, and pins stylix to release-26.05 (was unpinned master).
`nix flake check --no-build` and `nomarchy-eval-matrix` are both clean and
the full system builds (nixos-system-nomarchy-26.05).

Breaking-change fixes required by 26.05:
- stylix-compat: drop the `programs.neovim.initLua` shim — HM 26.05 declares
  it natively, so the shim was a duplicate-option error.
- swww was renamed to awww (binaries gone, no `init` subcommand). Dropped swww
  entirely and unified the wallpaper path on swaybg (the daemon this distro
  actually runs): nomarchy-theme-bg-next now delegates to nomarchy-theme-bg-set,
  swaybg added to the theme-engine script deps, swww removed from package lists.
- default config: add a placeholder `fileSystems."/"` — 26.05's systemd stage-1
  forces fsType during plain toplevel eval (the VM build overrides it).
- services.resolved: extraConfig removed, domains/fallbackDns renamed -> migrated
  to settings.Resolve.* (RFC42).
- systemd.sleep.extraConfig removed -> settings.Sleep.HibernateDelaySec (RFC42).
- X11 'virtio' video driver removed -> dropped from vm-guest.nix and
  nomarchy-live.nix (modesetting drives virtio-gpu).
- nomarchy-eval-matrix: define /persist + /home in the impermanence scenarios
  (26.05 maps fsType over every neededForBoot filesystem).
- README/MIGRATION/installer: stale swww references -> swaybg.

KNOWN BLOCKER (why this is on a branch, not main):
In a headless QEMU VM, Hyprland boots and inits GL (virgl) fine but is
OOM-killed after ~19s (3.4 GB peak). Likely a no-display-consumer artifact of
headless rendering (unthrottled frames), but a real Hyprland-26.05 memory
regression can't be ruled out without a real display. Verify on real hardware
(a fresh ISO install) before merging to main; if the desktop is stable there,
the OOM was the headless VM and this can merge.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

themes/engine/stylix-compat.nix

@@ -1,19 +1,16 @@
-{ config, lib, ... }:
+{ lib, ... }:
 
 # Compatibility shims for stylix target modules
 # Stylix unconditionally imports all target modules, which expect certain
 # program options to exist. This module defines stub options for programs
 # we don't use to prevent evaluation errors.
+#
+# Note: the neovim `initLua` shim was dropped at the 26.05 bump — Home Manager
+# now declares `programs.neovim.initLua` natively, so re-declaring it here is
+# both redundant and a duplicate-option error.
 
 {
   options = {
-    # Neovim: stylix uses initLua but home-manager uses extraLuaConfig
-    programs.neovim.initLua = lib.mkOption {
-      type = lib.types.lines;
-      default = "";
-      description = "Lua code to run at init (compatibility shim for stylix)";
-    };
-
     # OpenCode: stylix expects programs.opencode options
     programs.opencode = {
       tui = lib.mkOption {
@@ -28,8 +25,4 @@
       };
     };
   };
-
-  config = lib.mkIf (config.programs.neovim.initLua != "") {
-    programs.neovim.extraLuaConfig = config.programs.neovim.initLua;
-  };
 }